The present invention relates to a transient response data calculating method for calculating the transient response data of a tire during cornering or braking/driving based on a tire dynamic model that is built from at least one dynamic element parameter, a data processing method for calculating the value of a transient response parameter of a response function of the tire dynamic model that determines the behavior of transient response, and a tire designing method and vehicle motion predicting method that use the transient response calculating method. The present invention also relates to a tire cornering characteristic evaluating method and device for quantitatively evaluating the transient response characteristic of a tire's lateral force, which is generated in a tire rolling at a slip angle.
The recent increase in engine power has brought about the performance enhancement of passenger vehicle tires at a higher aspect ratio, with the intention of improving a vehicle's maximum cornering capability and responsiveness as well as traction performance. Despite such enhancement, it cannot be positively said that the steering stability in infinitesimal steering at high speed has been improved and, with the advancement of expressways, it is important to develop a tire that offers excellent infinitesimal steering stability at high speeds. A significant factor in the steering stability performance of a tire fit to a vehicle is the tire cornering characteristic, which is related to the response characteristic when the vehicle is subjected to quick steering movements.
The cornering characteristic of a tire is expressed as a response in the form of the tire's lateral force, cornering force, self-aligning torque (or the like) to an input to the tire such as load, slip angle, camber angle or slip ratio when the tire is subjected to quick steering movements. Lately, the demand for the development of a high-performance tire that exhibits good steering stability even with infinitesimal steering at high speed has created the need for a method and device that are capable of evaluating, quantitatively and precisely, the cornering characteristic of the tire alone.
Moreover, because a tire is the only thing between a vehicle and the road surface that transfers a force from the road surface to the vehicle, tires play an important role in today's automobile industry, which seeks advanced vehicle control for safe vehicle driving and the avoidance of danger. Therefore, it is necessary to analyze the tire's cornering characteristics.
The “actual ride feeling test,” in which a test tire is fit to a vehicle and an evaluator steers the vehicle so as to obtain information about steering stability, as sensed by the evaluator, is one of the conventional test methods for the evaluation of steering stability. The actual ride feeling test has an advantage in that information is obtained about steering stability in actual steering; however, the evaluation based on senses of an evaluator is not quantitative.
As a means of analyzing the tire cornering characteristic, there is a known method described in JP 2005-88832 A. This publication discusses a calculation in which the cornering characteristic of a tire in a steady state when a slip angle is given as time-series data is calculated based on a tire dynamic model built from multiple tire dynamic-element parameters. According to that publication, a tire can be efficiently designed through such a method.
Considering the above-mentioned tire dynamic model, a cornering characteristic in a steady state can be obtained by giving a slip angle, but it is not possible to reproduce a transient response during cornering, which changes with the slip angle given to the tire dynamic model in time series. Particularly in quick emergency steering for the avoidance of danger, the lateral force and self-aligning torque that the quick steering generates in a tire exhibit transient characteristics that differ from those in a steady state, and consequently it is meaningless to analyze vehicle motion from a cornering characteristic while in a steady state.
Additionally, today's vehicles generally use the anti-lock brake system (ABS), which controls the slip ratio on the basis of a few Hz so that the maximum braking power is always obtained. The braking power thus generated is therefore based on a characteristic in the transient state, which differs from that in a steady state. Therefore, it is meaningless to analyze the motion of a vehicle that has ABS from a longitudinal force in a steady state, which is calculated through the use of the above-mentioned tire dynamic model.
The evaluation of a tire dynamic characteristic with the use of an indoor cornering testing machine is also conducted in order to quantitatively and precisely evaluate the cornering characteristic of the tire alone. Iida, “Influence of Tire Dynamic Characteristics on Vehicle Motion Performance,” Automotive Engineering, 1984, No. 3, Vol. 38, p. 320 is given as an example. In an example of the conventional way of evaluating a cornering dynamic characteristic in order to evaluate a tire's dynamic characteristic through the use of an indoor cornering test machine, a tire is rolled on a contact patch at a constant speed. Slip-angle inputs are then applied to the tire at different frequencies in order to obtain a response characteristic in the form of a lateral force, cornering force, self-aligning torque or the like with respect to a distance frequency (distance frequency characteristic). The distance frequency characteristic is determined by the ratio of an angular speed ω of a slip angle input with respect to the tire's rolling speed.